docs: def triangle_area(e1, e2, e3):
      """
      Get the area of triangle formed by three vectors.
  
      Parameters are three three-dimensional numpy arrays representing
      vectors of triangle's edges in Cartesian space.
  
      :returns:
          Float number, the area of the triangle in squared units of coordinates,
          or numpy array of shape of edges with one dimension less.
  
      Uses Heron formula, see http://mathworld.wolfram.com/HeronsFormula.html.
      """
      # calculating edges length
      e1_length = numpy.sqrt(numpy.sum(e1 * e1, axis=-1))
      e2_length = numpy.sqrt(numpy.sum(e2 * e2, axis=-1))
      e3_length = numpy.sqrt(numpy.sum(e3 * e3, axis=-1))
      # calculating half perimeter
      s = (e1_length + e2_length + e3_length) / 2.0
      # applying Heron's formula
      return numpy.sqrt(s * (s - e1_length) * (s - e2_length) * (s - e3_length))